Solved

Casting From Thread Safe Class

Posted on 1999-01-27
1
223 Views
Last Modified: 2013-11-20
I've got a class for data which I want to use in both a base CWinThread and also a worker thread. I've made a child class of the data class adding only a CMutex and Get and Set functions. Now bearing in mind that I must use CSingleLock or CMultiLock to protect my objects when the worker thread is running, what ought to happen when I cast from the thread safe data class to the thread unsafe data class?
0
Comment
Question by:gavinpat
1 Comment
 
LVL 1

Accepted Solution

by:
gvg earned 100 total points
ID: 1328385
If you have dataclass as such

Class A
{
public:
  int  mNumber
}

class B : public A
{
  CMutex  mLock;
  int GetNumber( void );
  void SetNumber( int number );
}

int B:GetNumber()
{
  CSingleLock lock( mLock );
  return mNumber;
}

void B:SetNumber( int number )
{
  CSingleLock lock( mLock );
  mNumber = number;
}

Now you must access the members through the Get & Set functions to make them thread safe no matter if you are using class A or class B.  This is because a direct access to the member does not lock the threadlock. You can however not access the Get & Set functions in class A since they aren't defined.  What you should do is this


class A
{
protected:
  int mNumber;
public:
  virtual int GetNumber( void );
  virtual void SetNumber( int number );
}

class B : public A
{
public:
  CMutex mLock;
  virtual int GetNumber( void );
  virtual void SetNumber( void );
}

Now you can impliment the Get & Set members for both class A and class B.  If you create a instance of class B and cast it to A you will be able to access the member throught the Get & Set function and the virtual keyword will garanty that if the class was created as class B you will use its functions after you cast it to class A so it will be thread safe.

I also made the data member "mNumber" as protected so it can not be accessed directly by other classes.

Tip:
If you program is running entierly in a single process you should use CCriticalSection instead of CMutex.  There is not diffrance between this two classes except that the Mutex can work across process boundaries and is therefor much slower than CCriticalSection.

0

Featured Post

Free Tool: Site Down Detector

Helpful to verify reports of your own downtime, or to double check a downed website you are trying to access.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
List out all word 7 320
CRON statement to run every 3 minutes except on Monday morning 12am to 2am 7 103
bigDiff challenge 17 126
Problem to App 4 99
In this article, I'll describe -- and show pictures of -- some of the significant additions that have been made available to programmers in the MFC Feature Pack for Visual C++ 2008.  These same feature are in the MFC libraries that come with Visual …
Have you tried to learn about Unicode, UTF-8, and multibyte text encoding and all the articles are just too "academic" or too technical? This article aims to make the whole topic easy for just about anyone to understand.
This video will show you how to get GIT to work in Eclipse.   It will walk you through how to install the EGit plugin in eclipse and how to checkout an existing repository.

821 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question